The Luer Taper is a standardized system of small-scale fluid fittings used for making leak-free connections between a male-taper fitting and its mating female part on medical and laboratory instruments, including hypodermic syringe tips and needles or stopcocks and needles. Named after the 19th century German medical instrument maker Hermann Wulfing Luer, it originated as a 6% taper fitting for glass bottle stoppers. Key features of Luer Taper connectors are defined in the ISO 594 standards. It is also defined in the DIN and EN standard 1707:1996 and 20594-1:1993.
There are two varieties of Luer Taper connections: Luer-Lok and Luer-Slip. Luer-Lok fittings are securely joined by means of a tabbed hub on the female fitting which screws into threads in a sleeve on the male fitting. Luer-Slip fittings simply conform to Luer taper dimensions and are pressed together and held by friction (they have no threads). Luer components are manufactured either from metal or plastic and are available from many companies worldwide.
As mentioned above, the Luer connectors are defined in the ISO 594 standard. This standard like many is written by the International Organization for Standardization (ISO), the worldwide federation of national standards bodies (ISO member bodies).
In the 1990s concern grew in the federation regarding the proliferation of medical devices fitted with Luer connectors and the reports of patient death or injury arising from misconnections that resulted in the inappropriate delivery of enteral solutions, intrathecal medication or compressed gases. Concerns regarding the use of Luer connectors with enteral feeding tubes and gas sampling and gas delivery systems were raised with the European Committee for Standardization (CEN/BT) and the European Commission. In November 1997 the newly created CHeF steering group set up a Forum Task Group (FTG) to consider the problem. The FTG produced CEN Report CR 13825, which concluded that there is a problem arising from the use of a single connector design for a number of incompatible applications. In a coronary care unit there are as many as 40 connectors on the medical devices used with a single patient. Therefore it is not surprising that misconnections are made. Medical devices have for many years followed the established principle of “safety under single fault conditions”. Simply stated this means that a single fault should not result in an unacceptable risk. This principle is embodied in the requirements of numerous medical device standards. Extending this principle to the application of Luer connectors, i.e. that misconnection should not result in an unacceptable risk to a patient the FTG recommended that Luer connectors should be restricted to medical devices intended to be connected to the vascular system or a hypodermic syringe. In addition, new designs of small-bore connectors should be developed for other applications, and these should be non-interconnectable with Luer connectors and each other.
In reaction to this defined need, during the past few years a new set of standards have been developed with the standard ISO/ICE 80369-(1); “Small-bore connectors for liquids and gases in healthcare applications” defining the general requirements for connectors used with fluids in the medical environment, where “Part 2” defines the specific connectors for “breathing systems and driving gases for respiratory use.” This category includes connectors for Capnography, which is the monitoring of the concentration or partial pressure of CO2 in respiratory cases.
In Part 2, the requirements for connectors used with breathing systems and driving gasses are provided including definition and dimensions of a recommended new connector for this purpose. In this document, the concept, shape and dimensions of the proposed connector fittings are similar to the original Luer connectors defined in ISO 594, but its dimensions are enlarged by some 30%, sufficiently in order that the newly proposed connector cannot be mated with its original version. The tapered Luer connector as defined in the original ISO 594 standard was retained for use with infusion systems only. In fact, a third connector design using the same concept and shape, but with smaller dimensions is defined for a third group of connectors intended for use with enteral applications. Again, the dimensions have been chosen so that inter-connectivity among different types of connectors is prevented.
Even in the era when ISO 594 was used to define Luer connectors for breathing systems, and consequently for Capnography applications, it was noted that the defined design for the Luer may not have been optimal for Capnography. Somewhat unique to Capnography, where accurate display of the CO2 waveform as created by ever changing inhalation and exhalation stages of breathing is necessary, major attention must be given to how the sampled breath is transferred from the patient to the measuring device. The sampling technique must ensure that the waveform fidelity and shape of the changing CO2 concentration is kept by using very constant laminar flow with an undisturbed wave-front. Such disturbances are magnified if the gas flow passes via rough tubing, liquid filters, or sections of varying diameter in the tubing, conduits or connectors, abrupt changes in direction and irregularities etc. A measure of merit for the system ability to transfer the sampled breath from the patient to the measuring sensor of the Capnograph is the system Rise Time (sometimes referred to as the response time). A fast rise time is indicative of a well designed transfer of the sampled breath, while a slow rise time is indicative of a poor transfer of the breath suffering from the disturbing features defined above.
It is noted in Patent application No. US 2008/0284167; Low volume fittings: that the defined shape and dimensions dictated by the ISO 594 standard do not lend themselves to providing a fast rise time because of inevitable changes in the gas flow conduit diameter of the mating connectors. This is a result of the fact that a preferred diameter for the internal conduit used for transmitting the sampled gas is 1 mm, especially for a Capnograph that uses low gas sampling flow rates, e.g. 50 ml/min. This is further worsened by material choice, since the common material used for producing these connectors is plastic as it is more economic and appropriate for disposable components With plastic it is difficult to control tolerances of the 6% tapered cone, and these differences in tolerance dictate differences in the matching and final position of the two mated fittings. The problem can be seen in FIG. 1 (A, B and C), which shows Luer connectors according to the prior art. Luer connector 10 includes a 6% tapered Luer male connector 12 and Luer female connector 14 having an inner a 6% tapered cone. When the matched fittings (Luer male connector 12 and Luer female connector 14) are coupled, there still remains a conduit section of length E that may change because of the inherent tolerances that are inevitable when producing mass production, plastic parts, for example, between E min (FIG. 1A), E avg. (FIG. 1B) and E max (FIG. 1C). These E values are defined in the standard and must be maintained when manufacturing Luer connector. E max, for that matter, may be defined as the largest (worst) length of conduit that is formed between the Luer male connector and Luer female connector that is still acceptable by the standard.
This drawback is increased considerably with the new pending standard, ISO/CD 80369-1.2, where as mentioned, the new dimensions proposed are even larger, creating an even larger change in diameters and consequently distorting further the wave-front and producing an even slower rise time. Tests performed with Aluminum connectors representative of the maximum, mean and minimum tolerances (see Table 1 hereinbelow) as defined in the new standard have shown up to a 180 msec increase in rise time, meaning a much slower rise time. Such an increase would mean that requirements and performance parameters for rise time defined in Capnograph specifications will become non-compliant.
TABLE 1Male and Female Aluminum Cones for Large LuerConnector Simulators Rise Time Tests:SamplesStandardParametersAluminium ConesLuersRangemaxmeanMinMeanLd.sp.int., mm 3.5 1.8~0.02.3Response Time188±1992±9  6±79±9Tested Samples:Aluminium Cones:Male - min & max deviations (ID = 5.2).Female - min & max deviations.Standard Luer Locks:Typical Male (ID = 4.0) and Female.Symbols for given dimensions:Ld.sp.int. - Male to Female Cones distanceinternal dimensions.Testing Conditions:Qsampl. ~50 mL/min.Amb.: 24° C.; 33%; 931 mBar.Testing Device:Capnosat Capnograph (tubing direct to sensor)(RT)Back. ~45 mSec - minimum Rise Timebackground.
An attempted solution to this problem is provided in patent application No. US 2008/0284167; Low volume fittings. However, this approach cannot be used to solve the issue while still remaining compliant to the new standard: ISO/CD 80369-1.2. For example; see FIGS. 1D and 1E showing a Luer connector 100 as described in patent application: No. US 2008/0284167. It is proposed to increase the length of the 6% tapered Luer male connector 102, with an elastomeric material 106 that protrudes away from Luer male connector 102 by a distance F away from top 108 to a distal surface 110. As a result, when the matched fittings (Luer male connector 102 and Luer female connector 104) are coupled, elastomeric (soft) material 106 is squeezed from distance F to distance E and a reduced length of large diameter is accomplished and the extended elastomeric material would prevent the previously inevitable region of larger diameter conduit and thereby reducing it to a minimum. Such a solution is not permissible with the new standard, since the extended elastomeric section of the tapered male Luer, and its reducing diameter with length (6% taper) could easily be pushed into the female connector of a smaller sized Luer. As explained, three sized Luers with similar 6% tapered cones are expected to be introduced, but their sizes are such that when rigid materials as required are used, a larger size Luer cannot mate with a smaller defined size. This would not be the case with the proposed solution in the said application (US 2008/0284167).
To prevent such miss-connection, the new standard requirements dictate the use of rigid materials as well as an absolute dimension for the diameter of the male and female cone edge i.e. the diameter of the female side input edge and male inserting edge noted with the letter “d” for the male side and “D” for the female side. FIG. 2 shows such small-bore connector and its corresponding dimensions (summarized in Table 2 herein below) as appeared in standard ISO/ICE 80369-2.
TABLE 2DimensionRef.DesignationMinimumNominalMaximuma: ISO/ICE 80369-2 - RESP-125 dimensions of male small-bore connector(dimensions are in mm unless otherwise indicated).aAngle of taper (degrees) (6% taper nominal)3.44°3.44°3.52°bThread angle of male lock fitting  50°50.0°  55°dDiameter at the tip of the male taper 6%4.8514.9024.953eLength of male taper8.5098.6368.763fInner diameter at the tip of the male taper 6%1.01.952.9hMajor diameter of internal thread of male lock9.0399.1669.293fitting (diameter at thread root)jMinor diameter of internal thread of male lock7.7477.8748.01fitting (diameter at thread crest)kThread width of male lock fitting at root1.061.191.32LLength of taper engagement5.085.085.70mWidth between thread flanks at root1.221.3501.48nWidth between thread flanks at crest1.831.962.08oThread lead, (mm per 360° revolution)4.955.085.21(Right-hand trapezoidal thread is double start,5.1 mm per revolution)pPitch on internal trapezoidal tread2.412.542.67qThread width of male lock fitting at crest0.460.580.71rProjection of nozzle from collar2.162.292.41sThread length from collar end of male lock fitting7.57.67.8uInner diameter at the fluid lumen (recommended)2.402.552.70wWidth of majr projections13.413.513.8xAngle of inner lumen taper of the male taper 6%1.80°2.00°2.20°yInner diameter at the end of the male taper 6%2.582.712.84zLength of inner lumen inside the male taper 6%9.89.910.0(f to y)b: ISO/ICE 80369-2 - RESP-125 dimensions of female small-bore connector(dimensions are in mm unless otherwise indicated).AAngle of female taper (6% taper nominal)3.35°3.44°3.44°BThread angle of female lock fitting55.0°60.0°60.0°DDiameter at the open of the female taper 6%4.7504.8695.004EDepth of female taper13.1913.3113.44—————HMajor diameter of external thread of female lock8.929.049.17fitting (diameter at thread crest)JMinor diameter of external thread of female lock7.647.777.90fitting (diameter at thread root)KThread width of female lock fitting at crest1.121.241.37LLength of taper engagement5.085.085.70MOutside width of lock thread at crest1.171.301.42NOutside width of lock thread at crest1.912.032.16OThread lead, (mm per 360° revolution) (Right-hand4.975.105.23trapezoidal thread is double start, 5.1 mm perrevolution)PPitch of external trapezoidal tread2.372.502.63QThread width of female lock fitting at root0.380.510.54—————SThread length from open end of the female taper 6%2.52.72.8UInner diameter at the fluid lumen (recommended)2.402.552.70WWidth of major projections11.411.611.7———————————————NR—not restrictedParticularly, the diameter at the open end of the female taper 6% is defined as “D”.The diameter at the tip of the male taper 6% is defined as “d”.
In addition to the issue of conduits with changing diameters that occur when connecting the Luer fittings that comply with the standard, and the slower rise times that they promote, a further issue with these type connectors, is that they may incur leaks that will introduce erroneously low CO2 concentrations measurements because of dilution. This is found more so with the Luer lock version, i.e. the version where correct mating is realized by screwing the two mating fittings together firmly. In the hospital and emergence environment, the number of tasks required and the limited time available together with the state of emergency often create a situation where connectors are not mated securely and firmly. This results, as mentioned in even larger regions of increased diameters as well as, in some cases leaks with their negative effect on the readings. Though the user is required to feel the positive feedback received when the fittings are screwed on correctly, the conditions in the medical environment often do not lend themselves for the user to be sensitive to this feedback.
Hence there is an important need to find an economical means for structuring and mating two fittings for use with Capnograph monitors and their patient interfaces that comply with all the relevant ISO standards, and that incur only a negligible and minor increase in rise time and will provide a means for permitting gas flow between them only when this condition has been realized without the need for the user to control it.
The foregoing examples of the related art and limitations related therewith are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent to those of skill in the art upon a reading of the specification and a study of the figures.